Automatic brake shoe adjuster



Dec. 27, 1949 J. H. PRATT ET AL 2,492,237

AUTOMATIC BRAKE SHOE ADJUSTER Filed May 7, 1947 IN VENTORS JAMES HENRYPRATT GiLBERT EDGAR MANLEY ATTOR NEY Patented Dec. 27, 1949 2,492,237AUTfiMA'IIC BRAKE SHOE ADJUSTER James Henry Pratt, Tanners Green,Wythall, and Gilbert Edgar Manley, Norton Curlieu, Wan- Wi'cli, EnglandApplication May 7, 1947, Serial No. 746,516 In Great Britain February19, 1947 2 Claims.

This invention has reference to improvements relating to brakes and isconcerned with brakes in which there is inter sed between the surface onwhich the braking efior't is to be exerted and an abutment means, a stomeans which cooperates with the abutment means for determining the offposition of the means for applying the braking effort and which isassociated frictionally with the said applying means in such a mannerthat the stop means aforesaid moves with the applying means both duringthe application of and upon the relieving of the braking pressure, but,as braking operations are performed, is capable of being displacedautomatically relatively to the applying means as wear of the applyingmeans takes place by an amount commensurate with the degree of such wearso that the stop means and abutment means (to-operate to arrest themovement "of the a plying means to the off position whenever asubstantially predetermined clearance obtains between the applying meansand the surface to be braked.

With brakes as aforesaid it has been experienced that where withdrawalof the applying means is effected by strong pull off springs it isnecessary to impose such a high frictional loading between the stopmeans and the brake applying means that the stop means is prone tosqueak and wear when it contacts the braking surface and also to markthe said surface and furthermore after wear of the braking surfaces hastaken place upon a subsequent application of the brakes there is atendency for the drag induced -on the brake applying means as thebraking pressure is applied to displace the stop means so that in someconstructions it may not contact the fixed abutment means when thebraking pressure is relieved.

The present invention has for its object to pro vide an improved andsimplified means which ensures a high frictional resistance between thestop means and the brake applying means when the said applying means isin the off position and only sufficient frictional resistance to ensurethat the stop means moves with the said applying means whenever the stopmeans is out of contact with the abutment means but without preventingdisplacement of the stop means in either direction relatively to theapplying means if such movement is required and provided of course thatthe displacing force is sufficient to overcome the aforesaid frictionalresistance.

According to the invention an improved brake as aforesaid ischaracterised in that the stop means -is mounted on a brake applyingmeans so as to be capable of displacement in either direction againstfrictional resistance whenever the stop means is out of contact with theabutment means ah'd in that when the stop means isin contact with theabutment means forces are set up which cause a binding between the stopmeans and its mounting on a brake applying means so bringing into playautomatically a high frictional resistance between the stop means andits mounting whenever the stop means is in contact with the abutmentmeans which ensures that move ment of the applying means to the "off"position is arrested when a predetermined clearance between the applyingmeans and the surface to be braked is attained.

The'invention will now be described with particular reference to theaccompanying drawings wherein:

Figure -l is a view partly in section and partly in elevationillustrating somewhat diagrammatically the invention as applied to anhydraulically actuated two shoe intern-ally expanding brake for motorvehicles, which in general is of known construction.

Figure 2 is a fragmentary view on an enlarged scale showing in plan butpartly sectioned, the stop means and mounting incorporated in Figure 1,and

Figure 3 is a fragmentary view partly in section and also on an enlargedscale showing the manner of mounting the stop means utilised in theeon-=- struction illustrated in Figures l and 2, the sec tion beingtaken on the plane indicated by the line 3-3 Figure 2 looking thedirection of the arrows to said line.

The brake as depicted the drawings incorporates two similar brake shoesBa, 4b the lower ends of which abut a rulcram about a pivet pin 5 fixedto the back plate '6. The upper ends :of the brake shoes 5a, ib abut theends of plungers Ta which are associated with oppositely acting pistonsI mounted in an hydraulic cylinder 8 to which hydraulic pressure isapplied by 'way of an inlet port 8a in the normal manner. The pistons iare provided with the usual hydraulic packings 9 and co-oper'ate with aspring l0 inter posed between the pistons which tends to force thepistons 1 apart.

The brake shoes 4a, 41) have fixed to the .periphery thereof linings 12of material having a high co eifi'cient of friction.

The web of the brake shoe via, which shoe serves as a leading shoeduring forward travel, hasssecured thereto a pin l3 having anintermediate elongated portion 13a which is of a rectangular shape incross section.

This elongated portion I3a is mounted within an elongated slot Ma formedin the arm Mb of a stop member M of substantially inverted L shape andthe said elongated portion I3a is of slightly lesser depth than thedepth of the slot Interposed between a washer I5 in abutment with thearm Mb and a washer l6 secured on the outer end of the pin I3 is a coilspring I'I, said spring I'I causing the arm Mb to be gripped between thesaid washer I6 and a cylindrical enlarged portion I3b arranged on theopposite side of the web to the washer I5 so that a frictionalresistance to axial displacement of the arm Mb is imposed by thepressure exerted by the washer I5 on the marginal portions bounding theslot I 411.

The pin I3 is also provided with a threaded portion which is engaged bya nut I8 so that the pin I3 may be secured to the web of the shoe Ad byclamping the said web between the enlarged portion I31) and the nut I8.

The outer end of the arm Mb has secured thereto a separately formedplunger portion Me which passes through a hole in the table of the shoe4a and through a hole in the frictional lining l2 associated therewith.

The depending limb Md of the stop member M is adapted to abut theinwardly directed tapered portion I911, of a pin I9 having a screwthreaded portion mounted in a screw box 6a associated with the backplate 6, said pin I9 also having an externally squared portion I9b forthe reception of a tool whereby the said taper pin I9 can be adjustedrelatively to the back plate 6 as required.

The tapered pin I9 is adjusted initially so that when the arm Md is incontact therewith the distance between the centre of the elongatedportion I3a and the outer end of the plunger portion Me is less than thedistance between the centre of the elongated portion and the surface tobe braked by an amount corresponding to the clearance required to bemaintained between the applying means and the surface to be braked whenthe applying means is in the off position. The distance between thecentre of the projecting portion I30, and the outer end of the plungerMc defines the efiective length of the arm Mb.

Thus subject to the light frictional resistance to displacement imposedby the spring loaded washer l5 the stop member 54 is displaceable towardand away from the drum 20 whenever the depending limb Md is out ofcontact with the tapered abutment portion I9a of the pin I9 but wheneverthe brake shoes 4a, 4b are retracted by the pull ofi spring Ii thethrust exerted between the lower end of the depending limb Md of thestop member M and the abutment pin I9 gives rise to a couple acting atthe ends of the elongated portion I3a. As a consequence whenever thedepending limb Md of the stop member M is in contact with the taperedabutment portion I9a of the pin I9 the forces induced effect a cantingof the limb Mb of the stop member M relatively to the elongated portionI3a of the pin l3, see Figure 3 which occasions a binding between thesaid elongated portion I3a and the top and bottom walls of the slot Mawhich is sufiicient to prevent displacement of the stop memberrelatively to the brake shoe 4a despite the effort of the pull ofispring II.

Preferably the ratio in length of the distance between the point ofcontact between the tapered portion I96: and the depending limb Md ofthe stop member M and the pin I3 and between the said pin I3 and theplace where the plunger I40 projects through the table of the brake shoela is in the order of 3 or 4-1.

The frictional resistance imposed by the spring loaded washer I5 isprovided in order to ensure that the stop member I4 shall move with thebrake shoe 4a whenever the said stop member M is out of abutment withthe tapered portion [9a and is only required to be just sufficient forthis purpose.

An automatic adjustment means according to the invention is not prone tosqueaking due to contact between the stop member M and the brake drum 2Eand wear due to contact between the brake drum 20 and the stop member Mis minimized since on the application of a brake subsequent to wear ofthe braking surfaces the drag exerted on the then projecting end of theplunger I 40 effects a canting of the stop member Hi relatively to theelongated portion I3a of the pin is whereby the axis of the elongatedslot Ma tends to approach coincidence with the axis of the elongatedportion I30, so that inward displacement of the stop member M ispermitted and so that when the brakes are subsequently returned to theOE position and the stop member M locked by contact with the taperedportion I9a the predetermined clearance between the frictional liningsI2 and the brake drum 20 is maintained.

We claim:

1. An automatic brake adjustor for an internal expanding brake having acylindrical drum, a partially cylindrical shoe located interiorly of thedrum and pivotal relative thereto into and out of engagement therewith,means for forcing the shoe outwardly into engagement and resilientreturn means, the automatic adjustor comprising, in combination, anabutment mounted on an immovable portion of the brake, a pin mounted onsaid shoe and having a radially and axially extending flattened portion,an adjustable stop member mounted for cooperation between said pin andsaid abutment to position said shoe when in disengaged position, saidstop member having two angularly extending arms, one of said arms havinga longitudinally extending, parallel-sided slot cut therein, the memberbeing positioned over said pin with said flattened portion extendingloosely through the slot in said member, there being a slot through thecylindrical face of said shoe, the end of the slotted arm of said memberextending through the slot in said shoe and being engageable with theinner surface of said drum when said shoe is engaged therewith, the slotin the arm of said member being longer radially than the flattenedportion of said pin, the other arm of said member engaging said abutmentwhen said shoe is in disengaged position, and resilient means forholding said member on said pin.

2. An automatic adjustor according to claim 1 in which the stop memberis a fiat, bell-crank shaped lever with its faces lying in a verticalplane extending substantially perpendicularly to the axis of the brakedrum, the slotted arm extending generally radially of the brake and theabutment engaging arm extending at an angle thereto whereby engagementbetween the abutment and the engaging arm pivots said stop memberrelative to said pin, engaging the edges of the flattened portionthereof with the walls of the slot in the arm of said stop member andpreventing translation of said stop member radially of said brakerelative to said shoe.

JAMES HENRY PRATT. GILBERT EDGAR MANLEY.

REFERENCES CITED Number UNITED STATES PATENTS Name Date Kohr Nov. 28,1933 Bowen May 14, 1940 Loweke Apr. 21, 1942

